1. Field of the Invention
The present invention relates to a coil unit for wirelessly feeding or receiving power.
2. Description of the Related Art
Wireless power transmission technology that utilizes an electromagnetic induction effect between a primary (power feeding) coil and a secondary (power receiving) coil that face each other to transmit power without any mechanical contact such as a cable has attracted attention recently.
In the application of the wireless power transmission technology described above to devices for power supply of electric vehicles and the like, it is anticipated that the positional relationship between a power feeding coil installed in the ground or the like and a power receiving coil mounted in an electric vehicle or the like will not necessarily be constant. Such a displacement between the power feeding coil and the power receiving coil would cause a significant decease in magnetic coupling between the coils, which may entail the problem of low power transmission efficiency.
As a solution to the above problem is proposed in Japanese Unexamined Patent Application Publication No. 2010-172084 a non-contact electric power supply device technology in which a plurality of cores disposed in a plane with intervals therebetween are used. Japanese Unexamined Patent Application Publication No. 2010-172084 discloses that the plurality of cores serve as an enlarged core whose dimensions include the gaps, allowing the non-contact electric power supply device to be robust to displacement.
In the technique disclosed in Japanese Unexamined Patent Application Publication No. 2010-172084, however, since the plurality of cores are disposed in a plane with intervals therebetween, a magnetic flux that circulates in a location away from the coils is likely to occur, providing robustness to displacement. On the contrary, it is problematic that the unwanted leakage magnetic field is likely to be formed in a location away from the coils. In particular, in the application of wireless power transmission technology to a charger for a power electronic device such as an electric vehicle, a large current needs to flow through a coil in order to meet the demand for high-power transmission, causing an increase in the strength of a leakage magnetic field formed in a location away from the coils. This may cause electromagnetic interference which might affect nearby electronic equipment and so forth.